Optical coupling systems for optically coupling laser diodes to optical fibers

ABSTRACT

Optical coupling systems are provided. An optical coupling system includes a first optical fiber end having a first core, a second optical fiber end having a second core, and a laser diode optically coupled to the first core and the second core at an optical coupling location. The laser diode emits a light beam having an asymmetrical cross-sectional light beam profile comprising a fast axis diameter and a slow axis diameter. The fast axis diameter is longer than the slow axis diameter. Further, the first optical fiber end and the second optical fiber end are adjacently positioned along the fast axis diameter of the asymmetrical cross-sectional light beam profile of the laser diode at the optical coupling location such that the first core and the second core are within the asymmetrical cross-sectional light beam profile at the optical coupling location.

This application is a divisional of U.S. patent application Ser. No. 15/737,596, filed on Jun. 2016, ch is a 371 of International Application No. PCT/US16/37539, filed on Jun. 15, 2016, which claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/181,396, filed on Jun. 18, 2015, the content of which is relied upon and incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present specification generally relates to optical coupling systems and, more particularly, to optical coupling systems for optically coupling a laser diode to a plurality of optical fiber ends.

BACKGROUND

Optical fibers may be utilized in a variety of diverse applications in which light from a light source, such as a laser diode, is propagated along a length of the optical fiber. In some applications, such as lighting, signage, biological applications, etc. Light diffusing optical fibers may be utilized such that light propagating along the length of the light diffusing optical fiber is scattered radially outward along a length of the fiber.

Accordingly, a need exists for optical coupling systems for optically coupling laser diodes to a plurality of optical fibers, such as light diffusing optical fibers.

SUMMARY

In one embodiment, an optical coupling system includes a first optical fiber end having a first core, a second optical fiber end having a second core, and a laser diode optically coupled to the first core of the first optical fiber end and the second core of the second optical fiber end at an optical coupling location. The laser diode emits a light beam having an asymmetrical cross-sectional light beam profile comprising a fast axis diameter and a slow axis diameter. The fast axis diameter is longer than the slow axis diameter. Further, the first optical fiber end and the second optical fiber end are adjacently positioned along the fast axis diameter of the asymmetrical cross-sectional light beam profile of the laser diode at the optical coupling location such that the first core and the second core are within the asymmetrical cross-sectional light beam profile at the optical coupling location

In another embodiment, an optical coupling system includes a laser diode emitting a light beam and a fiber housing ferrule configured to house a first optical fiber end and a second optical fiber end. The fiber housing ferrule includes a ferrule body having a light input end opposite a light output end, a first fiber housing hole extending between the light input end and the light output end at a first angle relative to a longitudinal axis of the fiber housing ferrule, and a second fiber housing hole extending between the light input end and the light output end at a second angle relative to the longitudinal axis of the fiber housing ferrule. The first fiber housing hole and the second fiber housing hole are spaced apart at the light output end. A separation distance between the first fiber housing hole and the second fiber housing hole decreases in a direction from the light output end toward the light input end. The first fiber housing hole is adjacent to the second fiber housing hole at the light input end. Further, the first fiber housing hole and the second fiber housing hole are optically coupled to the laser diode at the light input end such that when the laser diode emits the light beam, the first fiber housing hole and the second fiber housing hole are each positioned within a cross-sectional light beam profile of the light beam at the light input end.

In yet another embodiment, an optical coupling system includes a first light diffusing optical fiber end, a second light diffusing optical fiber end, a laser diode configured to emit a light beam, and a birefringent crystal. The birefringent crystal is disposed between the laser diode and both the first light diffusing optical fiber end and the second light diffusing optical fiber end. The birefringent crystal is configured to: split the light beam into a first light beam and a second light beam, direct the first light beam into the first light diffusing optical fiber end, and direct the second light beam into the second light diffusing optical fiber end.

These and additional features provided by the embodiments described herein will be more fully understood in view of the following detailed description, in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

FIG. 1 schematically depicts an optical coupling system including a laser diode optically coupled to a first optical fiber end and a second optical fiber end at an optical coupling location, according to one or more embodiments described herein;

FIG. 2 schematically depicts an optical coupling system including a laser diode optically coupled to opposing optical fiber ends of an individual optical fiber at an optical coupling location, according to one or more embodiments described herein;

FIG. 3 schematically depicts an optical coupling system including a laser diode optically coupled to a first transport optical fiber and a second transport optical fiber at an optical coupling location, according to one or more embodiments described herein;

FIG. 4 schematically depicts the optical coupling system of FIG. 1 further including a focusing lens positioned between the laser diode and the first and second optical fiber ends, according to one or more embodiments described herein;

FIG. 5 schematically depicts an optical coupling system including a laser diode optically coupled to a first optical fiber end and a second optical fiber end, each positioned within a fiber housing ferrule, according to one or more embodiments described herein;

FIG. 6 schematically depicts an optical coupling system including a laser diode optically coupled to opposing optical fiber ends of an individual optical fiber positioned within the fiber housing ferrule of FIG. 5, according to one or more embodiments described herein;

FIG. 7 depicts an isometric view of the fiber housing ferrule of FIGS. 5 and 6, according to one or more embodiments described herein;

FIG. 8 schematically depicts a side view of the fiber housing ferrule of FIGS. 5-7, according to one or more embodiments described herein; and

FIG. 9 schematically depicts an optical coupling system including a birefringent crystal positioned between a laser diode and a first and second optical fiber end, according to one or more embodiments described herein.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to optical coupling systems comprising a laser diode optically coupled to a plurality of optical fiber ends (e.g., a plurality of light diffusing optical fiber ends, a plurality of transport optical fiber ends, or the like). The laser diode is configured to emit a light beam along an optical pathway. In some embodiments, the light beam comprises a cross-sectional light beam profile, such as an asymmetrical cross-sectional light beam profile and the plurality of optical fiber ends may be optically coupled to the cross-sectional light beam profile at an optical coupling location. In some embodiments, two optical fiber ends may be adjacently positioned within the cross-sectional light beam profile at the optical coupling location. Some optical coupling systems described herein comprise a fiber housing ferrule having fiber housing holes configured to house and adjacently position optical fiber ends at a light input end. Some optical coupling systems described herein comprise a birefringent crystal configured to split a light beam emitted by the laser diode and direct portions of the light beam into two optical fiber ends.

Referring now to FIG. 1, a schematic view of an optical coupling system 100 is depicted. The optical coupling system 100 comprises a laser diode 110 configured to emit a light beam 112 along an optical pathway 102. The laser diode 110 may comprise any laser diode, for example, a multimode laser diode, single mode laser diode, a SiP laser diode, VCSEL laser diode, or the like. In some embodiments, the laser diode 110 is hermetically sealed within a TO package. In some embodiments, an emission point of the laser diode 110 may be spaced apart from an output window of the TO package by between about 0.5 mm and 1 mm, such as, for example 0.7 mm, 0.85 mm, or the like. The laser diode 110 is configured to emit a light beam 112 having a cross-sectional light beam profile 114. When the laser diode 110 is a multimode laser diode, the cross-sectional light beam profile 114 may have an asymmetrical shape, such as an ellipse, an oval, or the like. In other embodiments, the cross-sectional light beam profile 114 may be symmetrical, for example, circular. While only one laser diode 110 is depicted in FIG. 1, it should be understood that in other embodiments the optical coupling system 100 may comprise two or more laser diodes 110 positioned within a single TO package.

As depicted in FIG. 1, the cross-sectional light beam profile 114 comprises a fast axis diameter 116 and a slow axis diameter 118. When the cross-sectional light beam profile 114 is asymmetrical, the fast axis diameter 116 is longer than the slow axis diameter 118. In some embodiments, the ratio between the length of the fast axis diameter and the slow axis diameter is 3:2, 2:1, 3:1, or 4:1. In other embodiments, the fast axis diameter 116 and the slow axis diameter 118 may have different length relationships. In one example embodiment in which the laser diode 110 is positioned within a TO package, the light beam 112 may comprise a fast axis diameter 116 of about 562 μm and a slow axis diameter 118 of about 170 μm at the output window of the TO package. In alternative embodiments, when the cross-sectional light beam profile 114 is symmetrical, the fast axis diameter 116 and the slow axis diameter 118 comprise substantially the same diameter.

Referring still to FIG. 1, the optical coupling system 100 comprises a plurality of optical fiber ends 120 positioned within the optical pathway 102 of the laser diode 110 and optically coupled to the laser diode 110 at an optical coupling location 104. The laser diode 110 and the plurality of optical fiber ends 120 may be optically coupled by aligning the laser diode 110 and the plurality of optical fiber ends 120 such that at least some of the light beam 112 emitted by the laser diode 110 is received by each of the plurality of optical fiber ends 120. In some embodiments, the plurality of optical fiber ends 120 comprise a first optical fiber end 122 a having a first core 124 a and a first cladding 126 a and a second optical fiber end 122 b having a second core 124 b and a second cladding 126 b. In some embodiments, each of the plurality of optical fiber ends 120 may further comprise one or more of a coating, a sheath, or a jacket circumscribing the cladding 126 a, 126 b.

In some embodiments, the first optical fiber end 122 a is an end of a first optical fiber and the second optical fiber end 122 b is an end of a second optical fiber. In other embodiments, such as the embodiment depicted in FIG. 2, the first optical fiber end 122 a and the second optical fiber end 122 b are opposing ends of the same optical fiber. While the plurality of optical fiber ends 120 are described as comprising the first optical fiber end 122 a and the second optical fiber end 122 b, it should be understood that the plurality of optical fiber ends 120 may comprise more than two optical fiber ends. It should be understood that any number of optical fiber ends may be positioned within the optical pathway 102 of the laser diode 110 at the optical coupling location 104. Further, in some embodiments, the first and second optical fiber ends 122 a, 122 b may be butt coupled to the laser diode 110. For example, when the laser diode 110 is positioned within a TO package, the first and second optical fiber ends 122 a, 122 b may be butt coupled to the emission window of the TO package. Butt coupling the first and second optical fiber ends 122 a, 122 b to the laser diode 110 may provide a coupling efficiency of between about 50% and about 70%.

Referring now to FIGS. 1 and 2, the first optical fiber end 122 a and the second optical fiber end 122 b are adjacently positioned within the optical pathway 102 at the optical coupling location 104. When the laser diode 110 emits the light beam 112, the first optical fiber end 122 a and the second optical fiber end 122 b may be adjacently positioned within the cross-sectional light beam profile 114 of the light beam 112. In some embodiments, the first optical fiber end 122 a and the second optical fiber end 122 b are adjacently positioned along the fast axis diameter 116 of the cross-sectional light beam profile 114. The fast axis diameter 116 may be sized such that the first core 124 a and the second core 124 b are within the cross-sectional light beam profile 114 at the optical coupling location 104. For example, the fast axis diameter 116 may be greater than or equal to a sum of a core diameter D₁ of the first core 124 a and a core diameter D₂ of the second core 124 b.

In some embodiments, the first cladding 126 a and the second cladding 126 b may be removed along at least a portion of the first optical fiber end 122 a and the second optical fiber end 122 b, respectively, such that the first core 124 a and the second core 124 b are exposed along the portion of the first optical fiber end 122 a and the second optical fiber end 122 b. In such embodiments, the first core 124 a and the second core 124 b may be adjacently positioned, for example, within a threshold distance (e.g., about 25 μm) or in contact. In such embodiments, the fast axis diameter 116 may be greater than or equal to the sum of the core diameter D₁ of the first core 124 a and the core diameter D₂ of the second core 124 b. By providing a cross-sectional light beam profile 114 that has a fast axis diameter 116 greater than or equal to the sum of core diameters D₁ and D₂ at the optical coupling location 104, optical coupling loss between the laser diode 110 and the first and second optical fiber ends 122 a, 122 b may be minimized.

In embodiments in which the first and second claddings 126 a, 126 b circumscribe the first and second cores 124 a, 124 b at the optical coupling location 104, the fast axis diameter 116 may be greater than the sum of the core diameter D₁ and the core diameter D₂. For example, the difference between the fast axis diameter 116 and the sum of the core diameter D₁ and the core diameter D₂ may be greater than or equal to the sum of a cladding thickness C₁ of the first cladding 126 a and a cladding thickness C₂ of the second cladding 126 b such that the first core 124 a and the second core 124 b are within the cross-sectional light beam profile 114 at the optical coupling location 104.

In some embodiments, the plurality of optical fiber ends 120 may comprise ends of light diffusing optical fibers. The light diffusing optical fibers include a core comprising glass, such as silica. In some embodiments, the core comprises pure silica and in other embodiments the core comprises silica having one or more dopants, (e.g., Ge, Al, Ti, and/or P). The core may comprise a numerical aperture (NA) between about 0.1 and about 0.8 (e.g., 0.22, 0.45, 0.53, 0.55, 0.57, or the like). Further, the core may comprise a diameter of between about 150 μm and about 200 μm, (e.g., 160 μm, 170 μm, 180 μm, or the like). The light diffusing optical fibers also include a cladding comprising a material having a low refractive index. The cladding may include a low index polymer such as ultraviolet (UV) curable or thermally curable acrylate, fluoroacrylate, or silicone. By providing a cladding surrounding the core, a waveguide may be formed having a high NA. In some embodiments, the diameter of the cladding may comprise between about 80 μm and 250 μm (e.g., 120 μm, 180 μm, 230 μm, or the like).

In embodiments in which the plurality of optical fiber ends 120 are ends of light diffusing optical fibers, the light diffusing optical fibers may further comprise a plurality of periodic or non-periodic nano-sized structures and/or voids positioned within the core or at a core-cladding boundary. In operation, the light diffusing optical fibers are configured to scatter light away from the core and through an outer surface of the cladding via the nano-sized structures. Light diffusing optical fibers are configured to radiate light along their length. In some embodiments, the light diffusing optical fibers further comprise an optional coating that surrounds the cladding, for example, a polymer coating such as an acrylate-based or silicone based polymer, or a fluorescent material that generates one or more colors when light diffuses through the coating.

Still referring to FIG. 1, in some embodiments, the first optical fiber end 122 a is an end of a first light diffusing optical fiber and the second optical fiber end 122 b is an end of a second light diffusing optical fiber. In other embodiments, such as the embodiment depicted in FIG. 2, the first optical fiber end 122 a and the second optical fiber end 122 b are opposing ends of the same light diffusing optical fiber. By optically coupling opposing ends of the same light diffusing optical fiber to the laser diode 110, light propagates into both ends of the light diffusing optical fibers. This provides a more uniform illumination along the length of the light diffusing optical fiber because each end of the light diffusing optical fiber receives substantially equivalent power components of the light beam 112.

Referring now to FIG. 3, the first optical fiber end 122 a may comprise a first transport optical fiber 130 a and the second optical fiber end 122 b may comprise a second transport optical fiber 130 b. The first and second transport optical fibers 130 a, 130 b may comprise a length of transmissive optical fiber configured to receive light at a light receiving end 131 a, 131 b and output light at a fiber coupling end 133 a, 133 b with minimal attenuation. The light receiving ends 131 a, 131 b are positioned opposite the fiber coupling ends 133 a, 133 b. Further, the fiber coupling ends 133 a, 133 b of the first and second transport optical fibers 130 a, 130 b may be coupled to additional optical fibers. For example, as depicted in FIG. 3, the fiber coupling end 133 a of the first transport optical fiber 130 a may be optically coupled, for example, abutted, to a third optical fiber 132 a and the fiber coupling end 133 b of the second transport optical fiber 130 b may be optically coupled, for example, abutted, to a fourth optical fiber 132 b. The third optical fiber 132 a and the fourth optical fiber 132 b may each comprise any optical fiber. In some embodiments, the third optical fiber 132 a and the fourth optical fiber 132 b are light diffusing optical fibers. In some embodiments, the third optical fiber 132 a and the fourth optical fiber 132 b may be opposing ends of a single light diffusing optical fiber. In alternative embodiments, the third optical fiber 132 a may comprise a third transport optical fiber, the fourth optical fiber 132 b may comprise a fourth transport optical fiber, and light output ends of the third transport optical fiber and the fourth optical fiber may in turn be optically coupled to ends of separate light diffusing optical fibers or to opposing ends of a single light diffusing optical fiber. It should be understood that any number of transport optical fibers are contemplated.

Referring now to FIG. 4, a focusing lens 106 may be positioned within the optical pathway 102 between the laser diode 110 and the first and second optical fiber ends 122 a, 122 b. The focusing lens 106 may comprise any focusing lens 106 that is configured to focus the light beam 112 into the first optical fiber end 122 a and the second optical fiber end 122 b. For example, the focusing lens 106 may comprise a spherical lens, an aspheric lens, a cylindrical lens, an anamorphic lens, a gradient index (GRIN) lens, a diffractive lens, a kinoform lens, or the like. In some embodiments, additional focusing lenses 106 may be contemplated. Positioning the focusing lens 106 within the optical pathway 102 between the laser diode 110 and the first and second optical fiber ends 122 a, 122 b may provide a coupling efficiency of between about 70% and about 90%. It should be understood that one or more focusing lens 106 may be optically disposed within the optical pathway 102 of any of the embodiments described herein, such as between the laser diode 110 and the optically coupled optical fiber ends of FIGS. 1-3 described above and of FIGS. 5-9 described below.

Referring now to FIGS. 5-8, the optical coupling system 100 may further comprise a fiber housing ferrule 150 having a first fiber housing hole 160 a configured to house the first optical fiber end 122 a and a second fiber housing hole 160 b configured to house the second optical fiber end 122 b. In some embodiments, such as the embodiment depicted in FIG. 5, the first optical fiber end 122 a is an end of a first optical fiber and the second optical fiber end 122 b is an end of a second optical fiber. In other embodiments, such as the embodiment depicted in FIG. 6, the first optical fiber end 122 a and the second optical fiber end 122 b are opposing ends of the same optical fibers. The first and second optical fiber ends 122 a, 122 b may comprise ends of any type of optical fiber, such as transport optical fibers, light diffusing optical fibers, or the like. In some embodiments, the first and second optical fiber ends 122 a, 122 b are adhered within the first and second fiber housing holes 160 a, 160 b, for example, using a transparent optical adhesive with a refractive index that is substantially similar to the refractive index of the cladding 126 a, 126 b.

As depicted in FIGS. 5-8, the ferrule body 152 of the fiber housing ferrule 150 has a light input end 154 opposite a light output end 156 and a longitudinal axis 151 extending between the light input end 154 and the light output end 156. In some embodiments, the ferrule body 152 may comprise a cylindrical rod, as shown in the isometric view in FIG. 7. However, in other embodiments, the ferrule body 152 may have a different shape, such as in embodiments in which the ferrule body 152 has a rectangular, triangular, elliptical, polygonal, or irregular cross-section. In some embodiments, the ferrule body 152 is optically transparent to visible light and UV light. In other embodiments, the ferrule body 152 may be translucent or opaque. In some embodiments, the ferrule body 152 is formed from a low index material such as a polymer, a plastic (e.g., fluorinated ethylene propylene (FEP)), or the like. In some embodiments, the ferrule body 152 is formed from glass (e.g., silica or the like), metal, or ceramic.

Still referring to FIGS. 5-8, the first fiber housing hole 160 a extends between the light input end 154 and the light output end 156 at a first angle α₁ relative to the longitudinal axis 151 and the second fiber housing hole 160 b extends between the light input end 154 and the light output end 156 at a second angle α₂ relative to the longitudinal axis 151. In some embodiments, the first angle α₁ and the second angle α₂ are the same angle such that the first fiber housing hole 160 a and the second fiber housing hole 160 b extend symmetrically relative to the longitudinal axis 151. In some embodiments, the first angle α₁ and the second angle α₂ are different angles. In some embodiments, the first angle α₁ and the second angle α₂ are in the range from about 1°-25°. In some embodiments, one or more of the first angle α₁ and the second angle α₂ are 5°, 10°, 15°, or the like. As best shown in FIGS. 5-6, the first fiber housing hole 160 a and the second fiber housing hole 160 b are spaced apart at the light output end 156 by a separation distance s. The separation distance s decreases in a direction from the light output end 156 toward the light input end 154 such that the first fiber housing hole 160 a is adjacently positioned to the second fiber housing hole 160 b at the light input end 154, as shown in FIGS. 5-8. Accordingly, in this embodiment, when the first and second optical fiber ends 122 a, 122 b are positioned in the first and second fiber housing holes 160 a, 160 b, respectively, the first core 124 a and the second core 124 b may be adjacently positioned at the light input end 154, for example, within a threshold distance (e.g., about 25 μm) or in contact.

Still referring to FIGS. 5-8, in some embodiments, the first fiber housing hole 160 a and the second fiber housing hole 160 b are optically coupled to the laser diode 110 at the light input end 154 such that when the laser diode 110 emits the light beam 112, the first fiber housing hole 160 a and the second fiber housing hole 160 b are each positioned within the cross-sectional light beam profile 114. As stated above with respect to FIGS. 1-4, the cross-sectional light beam profile 114 may be asymmetrical. In embodiments in which the cross-sectional light beam profile 114 is asymmetrical, the first fiber housing hole 160 a and the second fiber housing hole 160 b may be positioned along the fast axis diameter 116 of the cross-sectional light beam profile 114 at the light input end 154 in the manner described above with respect to FIGS. 1-4. As depicted in FIGS. 5-6, the first optical fiber end 122 a may be positioned within the first fiber housing hole 160 a and the second optical fiber end 122 b may be positioned within the second fiber housing hole 160 b such that the light beam 112 may propagate into the first optical fiber end 122 a and the second optical fiber end 122 b. In alternative embodiments, the focusing lens 106 of FIG. 4 may be positioned between the laser diode 110 and the light input end 154.

As depicted in FIGS. 5, 6, and 8, the first fiber housing hole 160 a may comprise a first core receiving portion 162 a and the second fiber housing hole 160 b may comprise a second core receiving portion 162 b. The first and second core receiving portions 162 a, 162 b extend from the light input end 154 toward the light output end 156. The first and second core receiving portions 162 a, 162 b also extend along the first and second fiber housing holes 160 a. 160 b, respectively, and comprise a diameter that is smaller than a diameter of the first and the second fiber housing holes 160 a, 160 b. Further, the first and second core receiving portions 162 a, 162 b are sized to receive the first and second cores 124 a, 124 b of the first and second optical fiber ends 122 a, 122 b, respectively. As depicted in FIGS. 5 and 6, the first and second core receiving portions 162 a, 162 b converge at the light input end 154 such that the first and second cores 124 a, 124 b of the first and second optical fibers ends 122 a, 122 b are in contact at the light input end 154 when positioned within the first and second fiber housing holes 160 a, 160 b.

In some embodiments, the first and second core receiving portions 162 a, 162 b each comprise a length that is less than a length of the first and second fiber housing holes 160 a. 160 b. For example, the first and second core receiving portions 162 a, 162 b may extend from the light input end 154 to a termination location 164 a, 164 b positioned between the light input end 154 and the light output end 156. The first and second core receiving portions 162 a, 162 b may terminate with first and second abutment shoulders 166 a, 166 b positioned at the termination locations 164 a, 164 b. The first and second abutment shoulders 166 a, 166 b are configured to abut the first and second cladding 126 a, 126 b, respectively, of partially stripped first and second optical fiber ends 122 a, 122 b. Further, as depicted in FIG. 8, the first and second fiber housing holes 160 a, 160 b may include first and second fiber insertion regions 168 a, 168 b located at the light output end 156 of the ferrule body 152. The first and second fiber insertion regions 168 a, 168 b may be frusto-conical in shape to aid in guiding the first and second optical fiber ends 122 a, 122 b into the first and second fiber housing holes 160 a, 160 b.

Referring still to FIGS. 5, 6, and 8, the first and second core receiving portions 162 a, 162 b are circumscribed by a first and second cladding matching region 167 a, 167 b. The first and second cladding matching region 167 a, 167 b may be substantially filled with a cladding matching material comprising a refractive index that matches the refractive index of the first and second cladding 126 a, 126 b. In some embodiments, the cladding matching material comprises a low refractive index epoxy that is UV curable and/or thermally curable.

In some embodiments, the first and second fiber housing holes 160 a, 160 b are configured to receive light diffusing optical fiber ends. In such embodiments, the diameter of each fiber housing hole 160 a, 160 b may be substantially equivalent (e.g., within a threshold distance of about 25 μm) to the diameter of the cladding 126 a, 126 b of the light diffusing optical fiber, for example, about 230 μm. Additionally, the diameter of the first and second core receiving portions 162 a, 162 b may be substantially equivalent (e.g., within a threshold distance of about 25 μm) to the diameter of the first and second cores 124 a, 124 b of the light diffusing optical fibers, for example, about 170 μm. In such embodiments, the refractive index of the cladding matching material positioned within the first and second cladding matching regions 167 a, 167 b may comprise a refractive index that is substantially the same as the refractive index of the light diffusing optical fiber cladding.

Referring again to FIGS. 5-8, the fiber housing ferrule may be fabricated by first providing a rod of a low index clear fluorinated plastic, such as FEP, and drilling first and second fiber housing holes 160 a, 160 b having first and second core receiving portions 162 a, 162 b into the rod. Next, the first and second cladding matching regions 167 a, 167 b of the first and second core receiving portions 162 a, 162 b are filled with the cladding matching material. The first and second optical fiber ends 122 a, 122 b are then cleaved, stripped to expose the first and second cores 124 a, 124 b, and inserted into the first and second fiber housing holes 160 a, 160 b. Next, the cladding matching material is UV cured or thermally cured from the light input end 154, the light output end 156, or a side of the ferrule body 152. Finally, the light input end 154 is polished. In some embodiments, the fiber housing ferrule 150 may be pre-shaped or fabricated for ease of use and integration into the TO package of the laser diode 110.

Referring now to FIG. 9, some embodiments of an optical coupling system 100 may include a birefringent crystal 170 positioned in the optical pathway 102 between the laser diode 110 and both the first optical fiber end 122 a and the second optical fiber end 122 b, which may be ends of a first light diffusing optical fiber and a second light diffusing optical fiber (as depicted in FIG. 9) or may be opposing ends of a single light diffusing optical fiber. The birefringent crystal 170 may be configured to: split the light beam 112 into a first light beam 112 a (e.g., an ordinary ray) and a second light beam 112 b (e.g., an extraordinary ray); direct the first light beam 112 a into the first optical fiber end 122 a (e.g., into the first core 124 a); and direct the second light beam into the second optical fiber end 122 b (e.g., into the second core 124 b). In some embodiments, the first light beam 112 a may be directed into an end of a light diffusing optical fiber and the second light beam 112 b may be directed into an opposing end of the same light diffusing optical fiber. In some embodiments, one or more focusing lenses 106 may be positioned within the optical pathway 102, for example, between the laser diode 110 and the birefringent crystal 170, to direct the light beam 112 into the birefringent crystal 170. Alternatively or additionally, one or more focusing lenses 106 may be positioned between the birefringent crystal 170 and the first and/or second optical fiber ends 122 a, 122 b to direct the first light beam 112 a into the first optical fiber end 122 a and/or direct the second light beam 112 b into the second optical fiber end 122 b.

The birefringent crystal 170 may comprise any birefringent material, for example, YVO₄, TiO₂, LiNBO₃, CaCO₃, or the like. In some embodiments, the birefringent crystal 170 may comprise an optical axis of about 45°. In other embodiments, the birefringent crystal 170 may comprise any optical axis, for example, an optical axis less than 45° or an optical axis greater than 45°. Further, the birefringent crystal 170 comprises a propagation angle and may be rotated (e.g., processed) about the propagation angle to alter the respective power components of the first and second light beam 112 a, 112 b received by the first and second optical fiber ends 122 a, 122 b, respectively. In some embodiments, the birefringent crystal 170 may be rotated to a position with respect to the propagation angle such that the first and second light beams 112 a, 112 b comprise equivalent power components. In other embodiments, the birefringent crystal 170 may be rotated to a position with respect to the propagation angle such that the first and second light beams 112 a, 112 b comprise unbalanced power components. For example, it may be desired that the first optical fiber end 122 a receives a larger or smaller power component than the second optical fiber end 122 b. It should be understood that the power components of the first light beam 112 a and the second light beam 112 b may be tuned by altering the rotation of the birefringent crystal 170 with respect to the propagation angle of the birefringent crystal 170.

Further, a thickness of the birefringent crystal 170 along the optical pathway 102 affects the spacing between the first light beam 112 a and the second light beam 112 b. An example birefringent crystal 170 comprising a 10 mm thickness produces a separation between the first light beam 112 a and the second light beam 112 b of about 1 mm. Another example birefringent crystal 170 comprising a 2 mm thickness produces a separation between the first light beam 112 a and the second light beam 112 b of about 230 μm. Further, a cut angle of the birefringent crystal 170 may affect the spacing between the first light beam 112 a and the second light beam 112 b. It should be understood that the separation between the first light beam 112 a and the second light beam 112 b may be tuned by altering the thickness of the birefringent crystal 170 and/or altering the cut angle of the birefringent crystal 170.

It should now be understood that the optical coupling systems described herein include a laser diode optically coupled to a plurality of optical fiber ends. In some embodiments, the laser diode is configured to emit a light beam comprising a cross-sectional light beam profile, for example, an asymmetrical cross-sectional light beam profile. The plurality of optical fiber ends may be optically coupled to the cross-sectional light beam profile at an optical coupling location. The optical coupling system may further comprise a fiber housing ferrule having fiber housing holes configured to house and adjacently position optical fiber ends at a light input end. Further, the optical coupling system may comprise a birefringent crystal configured to split a light beam emitted by the laser diode and direct portions of the light beam into two optical fiber ends. The optical fiber coupling systems herein provide small and low cost systems of optically coupling a laser diode to multiple optical fiber ends by reducing the number of laser diodes needed to illuminate multiple optical fiber ends. The optical fiber coupling systems herein also facilitate optical coupling between a laser diode and opposing ends of a light diffusing optical fiber, which improves illumination uniformity along the length of the light diffusing optical fiber.

It is noted that the term “substantially” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. This term is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter. 

What is claimed is:
 1. An optical coupling system comprising: a first light diffusing optical fiber end; a second light diffusing optical fiber end; a laser diode configured to emit a light beam; and a birefringent crystal disposed between the laser diode and both the first light diffusing optical fiber end and the second light diffusing optical fiber end, wherein the birefringent crystal is configured to split the light beam into a first light beam and a second light beam, direct the first light beam into the first light diffusing optical fiber end, and direct the second light beam into the second light diffusing optical fiber end.
 2. The optical coupling system of claim 1, wherein the birefringent crystal comprises an optical axis of about 45°.
 3. The optical coupling system of claim 1, wherein the birefringent crystal comprises YVO₄.
 4. The optical coupling system of claim 1, wherein the first light diffusing optical fiber end and the second light diffusing optical fiber end comprise ends of an individual light diffusing optical fiber.
 5. The optical coupling system of claim 1, wherein the first light beam comprises an ordinary ray and the second light beam comprises an extraordinary ray.
 6. The optical coupling system of claim 1, wherein the first light diffusing optical fiber end comprises a first core, and wherein the birefringent crystal is configured direct the first light beam into the first core.
 7. The optical coupling system of claim 1, wherein the second light diffusing optical fiber end comprises a second core, and wherein the birefringent crystal is configured direct the first light beam into the second core.
 8. The optical coupling system of claim 1, further comprising one or more focusing lenses positioned between the laser diode and the birefringent crystal.
 9. The optical coupling system of claim 1, further comprising one or more focusing lenses positioned between the birefringent crystal and one or both the first optical fiber end and the second optical fiber end.
 10. The optical coupling system of claim 1, wherein the birefringent crystal comprise a birefringent material selected from the group consisting of YVO₄, TiO₂, LiNBO₃, and CaCO₃.
 11. The optical coupling system of claim 1, wherein the birefringent crystal comprises an optical axis less than 45°.
 12. The optical coupling system of claim 1, wherein the birefringent crystal comprises an optical axis greater than 45°.
 13. The optical coupling system of claim 1, wherein the birefringent crystal comprises a propagation angle, wherein the first and second light beam comprise a power component, and wherein the birefringent crystal may be rotated about the propagation angle to alter one of or both of the power component of the first light beam and the second light beam received by the first and second optical fiber ends.
 14. The optical coupling system of claim 13, wherein the birefringent crystal may be rotated to a position with respect to the propagation angle such that the first and second light beams comprise equivalent power components.
 15. The optical coupling system of claim 13, wherein the birefringent crystal may be rotated to a position with respect to the propagation angle such that the first and second light beams comprise unbalanced power components.
 16. The optical coupling system of claim 13, wherein the birefringent crystal may be rotated to a position with respect to the propagation angle such that the first optical fiber end receives a larger or smaller power component than the second optical fiber end.
 17. The optical coupling system of claim 1, wherein the birefringent crystal comprises a thickness of about 10 mm thickness and the first light beam and the second light beam are separated by about 1 mm.
 18. The optical coupling system of claim 1, wherein the birefringent crystal comprises a thickness of about 2 mm thickness and the first light beam and the second light beam are separated by about 230 μm.
 19. The optical coupling system of claim 1, wherein the birefringent crystal comprises a cut angle that changes the spacing between the first light beam and the second light beam.
 20. The optical coupling system of claim 1, wherein the laser diode is optically coupled to the first light diffusing optical fiber end and the second light diffusing optical fiber end. 